The present invention relates to making 2,3-dihalopropanols.
2,3-Dihalopropanols are usually represented by: ##STR1## wherein: each "X" is independently a halogen atom; and
each "R" is independently a hydrogen atom or an organic group. 2,3-Dichloropropanol is the most commonly used member of the class. PA1 each "R" is independently hydrogen or a lower (C.sub.1 to C.sub.6) hydrocarbyl group, is preferably hydrogen or a lower alkyl group, is more preferably hydrogen or a methyl group and is most preferably hydrogen.
2,3-Dihalopropanols are important intermediates in the manufacture of epihalohydrin. For instance, epichlorohydrin is usually made by a three-step process of:
(1) reacting propylene and chlorine to make allyl chloride; PA0 (2) reacting allyl chloride with hypochlorous acid to make a mixture of dichloropropanols; and PA0 (3) reacting the dichloropropanols with a strong base to make epichlorohydrin. PA0 (1) reacting acrolein with chlorine to form 2,3-dichloropropanal; PA0 (2) reacting 2,3-dichloropropanal with a secondary alcohol in the presence of a catalyst to form 2,3-dichloropropanol (transfer hydrogenation); and PA0 (3) dehydrochlorinating 2,3-dichloropropanol to make epichlorohydrin. PA0 (1) reducing 2,3-dihalopropanal to form 2,3-dihalopropanol as described in the first aspect of the invention; and PA0 (2) cyclizing 2,3-dihalopropanol to make epihalohydrin. PA0 G. E. Coates et al., Principles of Organometallic Chemistry, Methven & Co. Ltd, London, 1971; PA0 Charles M. Lukehart, Fundamental Transition Metal Organometallic Chemistry, Brooks/Cole Publishing Co., Monterey, Calif., 1985; George W. Parshall, Homogenous Catalysis, John Wiley & Sons, New York, 1980; PA0 B. J. Huberoff, Homogeneous Catalysis Industrial Applications and Implications, American Chemical Society, Washington, D.C. 1968; and Brian R. James, Homogeneous Hydrogenation, John Wiley & Sons, New York, 1973; all incorporated herein by reference.
This process makes large quantities of halogen-containing waste. For each mole of epichlorohydrin which is produced, at least about two moles of molecular chlorine are required. Each molecule of epichlorohydrin contains one atom of chlorine, and the remaining three atoms of chlorine are lost in the waste stream.
It has been proposed to make epihalohydrins by processes which are more efficient in their use of halogen. For instance, Furman et al. (U.S. Pat. No. 2,860,146 (Nov. 11, 1958)) proposed to make epihalohydrin by a three-step process of:
However, the costs associated with this process are too high for it to be economically feasible, due to the cost of recycling coproduct ketone back to alcohol and regenerating catalyst. Furthermore, Furman et al. teaches that "ordinary methods of catalytic hydrogenation cannot be used successfully for the reduction step of the new process because of the poor yields and for high consumption of catalyst in the reaction."
What is needed is an economical process to make dihalopropanols with reduced production of halogenated waste.